This invention relates to carbonate polymer compositions containing additives which act as flame retardants.
Carbonate polymers derived from reactions of dihydroxyorganic compounds, particularly the dihydric phenols, and carbonic acid derivatives such as phosgene, have found extensive commercial application because of their excellent physical properties. These thermoplastic polymers are suitable for the manufacture of molded parts wherein impact strength, rigidity, toughness, heat resistance and excellent electrical properties are required.
Unfortunately, however, these polymers exhibit a brief but definite burning time when contacted with an open flame. More importantly, as is often the case, the carbonate polymers contain stabilizers and other additives which are often more combustible than the unmodified carbonate polymer. As a result, the modified carbonate polymers frequently exhibit substantially poorer resistance to combustion than does the unmodified carbonate polymer.
In attempts to increase the combustion resistance of carbonate polymers including the modified forms thereof, it has been a common practice to employ monomeric phosphites, phosphoric acid esters, thiophosphoric acid esters containing halogenated alkyl radicals and halogenated organic compounds into the carbonate polymer. However, in order to obtain any noticeable improvement in combustion resistance, these additives have been employed in such large quantities that they often adversely affect many of the desirable physical and mechanical properties of the carbonate polymer.
It is also known that oligomeric compounds having the general formula: EQU H--[O--R--O--P(OR.sub.1)].sub.n --O--R--OH
wherein R is the divalent residue of a dihydric mononuclear phenol or dihydric polynuclear phenol, R.sub.1 is an alkyl, aralkyl, or alkaryl group having 1 to 25 carbons, and n is a number having an average value of 1-200, impart improved thermal stability to carbonate polymers copolymerized with such oligomeric compounds. Such compositions are described in more detail in U.S. Pat. No. 4,444,978.
Recently, for example as taught in U.S. Pat. No. 4,254,015; metal salts of aromatic sulfonamides are employed as fire retardant additives in order to retard the combustion of carbonate polymers which are exposed to a low temperature ignition source. Unfortunately, the use of such salts as ignition resistant additives to carbonate polymers can adversely affect the processing stability of the carbonate polymer. As a result, carbonate polymers containing such ignition resistant salt additives can exhibit undesirable molecular weight degradation and can adversely affect optical properties.
In view of the deficiences of the conventional fire retardant carbonate polymer compositions, it would be highly desirable to provide a carbonate polymer composition having improved resistance to burning when exposed to an ignition source, and which composition exhibits good molecular weight stability and optical stability upon processing.